If I remember correctly a bloodthirsty token was created every time the target took damage that turn. Now it's only if the unit was previously damaged and also takes more damage in the turn? That's a considerable nerf. Why?

BLOOD​ ​THIRSTY:​ After a unit with Blood Thirsty finishes resolving an attack that damaged an enemy unit which was damaged before the attack, the unit with Blood Thirsty gains a Blood token until the end of its next activation.

Previously, Bloodthirsty would only trigger off melee attacks. The current wording allows any attacks to grant a token, provided the other condition is met. It is worth noting that your description is wrong; Bloodthirsty is not turn dependent - it only cares that the target has taken damage at least once before. If the target is taking damage for the second+ time that game, then the attacking unit with Bloodthirsty gets a token.

Both Bloodthirsty and Killmarks were changed to allow any unit to generate the token, regardless of what their ability types were. Additionally, both abilities now require a little more planning to use. The net result is that both factions will see their units gain tokens slightly less often; though frankly they were the easiest tokens to get after Doctrine, so that's not a bad thing given how strong some of the Cadre abilities were.

I will point out that with the change that allows minions to activate before heroes, you can still load a hero unit with a blood token on the first turn, given favorable placement.

Not sure if you meant to necro this, Mikelnut, but the mechanic in question is no longer part of the 2.0 ruleset. The faction abilities that generated tokens were consolidated and all factions can create tokens in the same way (disacsrding at the start of your turn). This change balanced things out, and along with a number of other core mechanic changes, has resulted in a really tight and meaningful hand economy.